ESL Video Quiz: The food web

The food web
No matter where on Earth you go, living things
are connected to each other. From the tiniest of
organisms to the largest of creatures, all living
things need energy to survive. So where does that
energy come from? Well, matter and energy passes
from one organism to another, connecting living
things like links in a chain: a food chain!
Of course a food chain is not an actual chain.
It’s a way to talk about the relationships
between organisms and show how matter and energy
flow between living things. Every living thing on
Earth is part of a food chain, including you, and
most things are part of more than one.
All of the energy in Earth’s food chains comes
from the sun. The sun’s energy reaches the earth
as light and heat, and plants capture some of it
and convert it into food through photosynthesis.
Because plants make, or produce, their own food
from the sun’s energy, they are called
‘producers.’
Every food chain must begin with a producer – for
example, grass. That’s because animals cannot
create their own food. They must eat, or consume,
energy from other sources. That’s why animals are
called ‘consumers.’
The second link of food chain is a consumer that
eats plants – an herbivore. When an animal eats
plants, some of the energy the plant capture from
the sun is transferred into the animal’s body,
where it is used for things like moving,
breathing, and growing. An herbivore is called a
primary consumer. Primary means ‘first’, because
an animal eating plants is the first consumer in
the food chain! Let’s add a rabbit to our food
chain.
Next comes a secondary consumer, the second
consumer in the food chain. This consumer is a
carnivore, and gets their energy by eating other
animals. Maybe our rabbit will get eaten by a
fox. When the fox eats the rabbit, part of the
energy that the rabbit got from the grass is
transferred to the fox.
This is the end of this simple food chain. The
rabbit eats the grass, then the fox eats the
rabbit. The energy that came from the sun is
captured by the grass, transferred to the rabbit,
and then transferred to the fox.
Some food chain are longer than this one, but
there can’t be too many links in a food chain.
Each animal in the food chain uses up a lot of
energy from the previous level instead of passing
it on meaning that only about 10% of the energy
consumed by an animal will be passed on to the
next level.
Let’s take a look at a longer food chain that
also begins with grass. This time, let’s make our
primary consumer a grasshopper. The grasshopper
eats the grass, and then gets eaten by a
secondary consumer – a bluebird. Then the
bluebird gets eaten by a tertiary, or third-
level, consumer – a snake. The snake is eaten in
turn by an owl. The owl is the apex predator in
this food chain.
Apex predators are not hunted and eaten by any
animals. We say there are at the top of the food
chain. You probably recognize a lot of apex
predators like lions, sharks, eagle, and
crocodiles. Just because they don’t get eaten
doesn’t mean that they don’t contribute to the
food chain, however!
When an animal dies, their body is broken down by
decomposers. Decomposers are usually bacteria and
fungi that break down dead plants and animals
into nutrients in the soil that in turn help the
plants at the beginning of the food chain to
grow. It’s the circle of life.
Natural ecosystems usually have more complicated
food chains, however. A network of interconnected
food chains is called a food web. The arrows are
used to show which direction the energy flows and
help keep track of the connections between
organisms.
Now that you understand a little bit more about
food chains, see if you can find the connections
between living things around you!